1. Field of the Invention
This invention relates to devices for measuring flow rates, and more specifically to a flow meter having an undulating flexible membrane whose frequency is a function of volumetric flow.
2. Description of the Prior Art
The monolithic microprocessor has revolutionized process control technology, but it has not yet found widespread application in practical electrohydraulic systems. Heretofore, an obstacle to microprocessor controlled electrohydraulic systems was the absence of an inexpensive flow meter which would easily interface with digital logic.
One attempt to interface a flow meter with digital logic is described in U.S. Pat. No. 4,033,188, issued July 5, 1977, entitled "Linear Vortex-Type Flowmeter," which discloses an electronic data processing system for a vortex-type flowmeter wherein the fluid to be measured is directed past a vortex-producing element to induce fluidic variations whose frequency is a function of flow rate. These variations are detected by a sensor yielding a signal having an A-C component whose frequency represents the uncorrected flow rate and a D-C component magnitude represents the temperature of the fluid. In order to correct for the effect of temperature on the accuracy of the reading, the signal components are separated from each other and converted into corresponding digital values which are fed into the data processing system to which are also applied digital values representing the fluid characteristics, the system producing an output signal representing the true flow rate.
The above-described system is inherently analog and requires relatively complex electronic circuitry to interface with the digital circuitry associated with the microprocessor. Moreover, the system is sensitive to temperature variations which must be corrected. Accordingly, there is a need for a more simple and less expensive flow meter which is well adapted for digital logic interfacing.